Various electronic devices in which an organic electroluminescent element (hereinafter often referred to as “organic EL element”) is utilized, such as organic EL illuminators and organic EL displays, are being put to practical use in recent years. Since organic EL elements are low in applied voltage and in power consumption, emit light areally, and are capable of emitting light of three primary colors, application thereof to illuminators and displays is being investigated enthusiastically. Improvements in luminescent efficiency are desired for that purpose.
As a means for improving the luminescent efficiency, it has been proposed to use a phosphorescent material in the emission layer of an organic EL element so as to utilize the phenomenon in which the recombination of holes with electrons yields singlet excitons and triplet excitons in a ratio of 1:3 (non-patent documents 1 and 2). Widely known as the phosphorescent material are, for example, ortho-metalized iridium complex compounds such as bis(2-phenylpyridinato-N,C2′)iridium acetylacetonate (Ir(ppy)2(acac)), tris(2-phynylpyridinato-N,C2′)iridium (Ir(ppy)3), and tris(1-phenylisoquinoline-N,C2′)iridium (Ir(piq)3) (non-patent documents 3 and 4). In particular, iridium complex compounds which emit phosphorescent red light are disclosed in non-patent documents 3 to 5 and patent documents 1 to 3, and organic EL elements employing these iridium compounds have been produced.
It is known that there is a strong correlation between the luminescent quantum yield of an iridium complex compound and the luminescent efficiency of an organic EL element produced using the compound. It is therefore necessary that an iridium complex compound having a high luminescent quantum yield should be developed for obtaining an organic EL element having a high luminescent efficiency.